Perfluorovinylethers are useful monomers for the manufacture of various fluoropolymers, in particular thermoprocessable tetrafluoroethylene (TFE)-based plastics and elastomers.
Methods for manufacturing perfluorovinylethers are known in the art; said methods generally involve dehalogenation of suitable halofluoroether precursors in liquid phase in the presence of transition metals.
Thus, US 2007203368 (SOLVAY SOLEXIS SPA) 30.08.2007 discloses a liquid-phase process for the manufacture of perfluorovinylethers by dehalogenation of certain halofluoroethers in the presence of transition metals as zinc, copper, manganese or metal couples as Zn/Cu, Zn/Sn, Zn/Hg.
Nevertheless, processes of the prior art generally suffer from the disadvantage that significant amounts of metal halides aqueous solutions or muds are typically obtained as by-products (e.g. ZnCl2 solutions/muds are produced when a chlorofluoroether is dechlorinated over zinc). Separation of said by-products from target perfluorovinylethers and their handling and disposal are time-consuming, costly and very burdensome from an industrial point of view, as these muds are highly corrosive and possibly endowed with negative environmental impact.
Need was therefore felt in the art for a cost-effective industrial process for the manufacture of perfluorovinylethers overcoming the drawbacks of liquid phase processes of the prior art.
Catalytic hydrodechlorination of chlorofluorocarbons (CFCs) to selectively yield unsaturated compounds is known in the art. GB 698386 (UNION CARBIDE) 14.10.1953 and U.S. Pat. No. 2,685,606 (UNION CARBIDE) 03.08.1954 disclose gas-phase hydrodechlorination of CFC-113 to yield 1-chloro-1,2,2-trifluoroethylene (CTFE) over supported nickel catalysts at temperatures in the range from 400 to 475° C., catalytic performances being worse at lower temperatures.
Further, catalytic hydrodechlorination of CFCs to yield unsaturated compounds at relatively low temperatures is also known in the art. U.S. Pat. No. 5,068,473 (DU PONT DE NEMOURS) 26.11.1991 discloses selective gas-phase hydrodechlorination of CFC-113 to CTFE over 5 wt. % Re/C catalyst at 200° C. Also, MORI, Tohru, et al. Hydrodechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) over supported ruthenium and other noble metal catalysts. Catalysis Today. 2004, vol. 88, p. 111-120. discloses Ru-catalyzed gas-phase hydrodechlorination of CFC-113 to yield CTFE. Very high hydrogen/substrate molar ratios are taught as mandatory for obtaining selectively unsaturated compounds, this high hydrogen consumption making the process uneconomical.
Finally, OHNISHI, Ryuichiro, et al. Selective hydrodechlorination of CFC-113 on Bi- and TI-modified palladium catalysts. Applied Catalysis A: General 1994, vol. 113, p. 29-41. discloses selective gas-phase hydrodechlorination of CFC-113 to yield CTFE or 1,2,2-trifluoroethylene (TrFE) over palladium catalysts containing metal additives like, notably, Thallium at 200° C. U.S. Pat. No. 5,498,806 (DAIKIN INDUSTRIES) 12.03.1996 discloses gas-phase hydrodechlorination of CFC-113 to yield CTFE selectively over a TI/Ru catalyst (TI/Ru molar ratio is 2:1) at 200° C. These documents teach that using certain metal dopants, like, notably, the highly toxic TI, it is possible to selectively promote hydrodechlorination while suppressing hydrogenation activity of said catalysts.
Now the Applicant has surprisingly found that under certain conditions the catalytic hydrodehalogenation process can be advantageously applied to halofluoroethers to obtain perfluorovinylethers with high selectivity.